Rubbery polymers

ABSTRACT

DISCLOSED IS A METHOD FOR THE PREPARATION OF NEW AND USEFUL TRIBLOCK COPOLYMERS OF THE ABA TYPE, WHEREIN THE B-BLOCK IS A POLYSULFIDE AND THE A BLOCK IS A POLYMERIZABLE VINYL-SUBSTITUTED COMPOUND. FORMATION OF THE B BLOCK IS ACCOMPLISHED BY INITIATING CYCLIC SULFIDES WITH ORGANOLITHIUM COMPOUNDS AT CONDITIONS OF LOW TEMPERATURE, SUBATMOSPHERIC PRESSURE FREE FROM ACTIVE HYDROGENS AND COMPOUNDS SUCH AS WATER AND IN A POLAR SOLVENT. DEPENDING UPON THE INITIATOR SELECTED, THE RESULTING POLYSULFIDE WILL TERMINATE WITH EITHER OR BOTH ENDS POSSESSING A CARBANION WHICH IS CAPABLE OF INITIATING POLYMERIZATION OF SUBSEQUENTLY ADDED VINYL-SUBSTITUTED COMPOUNDS TO FORM THE A BLOCK. THUS EITHER AN AB COPOLYMER OR AN ABA TRIBLOCK COPOLYMER MAY BE FORMED.

United States Patent Olfice 3,804,922 Patented Apr. 16, 1974 3,804,922RUBBERY POLYMERS Lewis J. Fetters, Akron, Ohio, Rudolf F. Kammereck,State College, Pa., and Maurice Morton, Akron, Ohio, assignors to TheUniversity of Akron, Akron, Ohio No Drawing. Continuation-impart ofabandoned application Ser. No. 108,957, Jan. 22, 1971. This applicationDec. 29, 1972, Ser. No. 319,446

Int. Cl. C08f 33/08 US. Cl. 260-874 9 Claims ABSTRACT OF THE DISCLOSUREDisclosed is a method for the preparation of new and useful triblockcopolymers of the ABA type, wherein the B block is a polysulfide and theA block is a polymerizable vinyl-substituted compound. Formation of theB block is accomplished by initiating cyclic sulfides with organolithiumcompounds at conditions of low temperature, subatmospheric pressure freefrom active hydrogens and compounds such as water and in a polarsolvent. Depending upon the initiator selected, the resultingpolysulfide will terminate with either or both ends possessing acarbanion which is capable of initiating polymerization of subsequentlyadded vinyl-substituted compounds to form the A block. Thus either an ABcopolymer or an ABA triblock copolymer may be formed.

CROSS REFERENCE TO RELATED APPLICATION This application is acontinuation-in-part application of US. Ser. No. 108,957, filed Jan. 22,1971, now abancloned.

BACKGROUND OF THE INVENTION The present invention relates to a newmethod for the preparation of polymers of cyclic sulfides terminated bya carbanion at either or both ends. The polysulfide so prepared iscapable of initiating polymerization of vinylsubstituted monomers toform either block copolymers of the AB type or triblock copolymers ofthe ABA type.

The polymerization of cyclic sulfides and vinyl-substituted monomersinitiated by organolithium compounds is well known in the art.Thiiranes, cyclic sulfides having three membered rings, form a lithiumalkylthiolate which SUMMARY OF THE INVENTION It is therefore an objectof the present invention to provide a method for the polymerization ofthietanes, cyclic sulfides having four-membered rings, wherein a linearpolymer is formed terminated by a carbanion.

It is another object of the present invention to provide a method forthe preparation of a triblock copolymer of the ABA type wherein the Ablock is a vinyl-substituted polymer and the B block is a thietane.

It is a further object of the present invention to provide a method forthe polymerization of a thietane which is capable of initiatingpolymerization of a vinyl-substituted monomer at either or both ends toform block or triblock copolymers.

It is a still further object of the present invention to provide amethod for the preparation of ABA triblock copolymers utilizing mono anddifunctional organolithium catalysts.

It is yet another object of the present invention to provide a methodfor preparing triblock copolymers at conditions of low temperature andpressure.

It is yet another object of the present invention to prepare a triblockcopolymer having elastomeric properties with excellent azone resistanceand high temperature resistance.

It is a still further object of the present invention to prepare atriblock copolymer which is highly elastomeric without vulcanization,and which may be worked or processed as a thermosetting plastic.

These and other objects of the present invention and method will becomeapparent from the following specification and claims.

In general, it has now been found that at low temperatures ofapproximately C. and under high vacuum, approximately 10- torr, anorganolithium compound and a thietane, in a polar solvent, will react toform a carbanion species and ultimately a linear polymer which is thencapable of initiating polymerization of vinyl-substituted monomers ateither or both ends to form block or triblock copolymers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The organolithium compoundswhich initiate the polymerization of thietanes may be mono or dilithiumhaving the generic formulae RLi and LiRLi respectively where R isaliphatic, cycloaliphatic or aromatic or combinations thereof and rangesfrom 1 to about 20 carbon atoms. Preferred monolithium initiators aremethyllithium, ethyllithium, and the isomers of propyllithium andbutyllithium. The preferred dilithium initiators are the dilithiumadducts of 2,4-hexadiene, 1,1-diphenylethylene, cis or trans stilbene,isoprene, 2,3-dimethylbultadiene, a-methylstyrene and the like. Thepreferred amount of monolithium initiator ranges from 2.0 to 0.5millimoles/ grams of thietane. Thus, the molecular weight of the linearpolymer so produced will range between 40,000 and 1,000,- 000 with adesired molecular weight of approximately 50,000 to 200,000.

The thietanes which may be polymerized have the general formula:

where R is selected from the group consisting of alkyl, aryl, cycloalkylradicals and combinations thereof having from 1 to 9 carbon atoms andwhere R to R are selected from the group consisting of hydrogen andalkyl, aryl, cycloalkyl radicals and combinations thereof having from 0to 9 carbon atoms. The total of I 1+ 2+ s+ 5+ s should not exceed 24carbon atoms. As one skilled in the art will recognize, there are manythietanes available. However, according to the present method, onlythose thietanes which are soluble when polymerized will work. Generally,it has been found that thietanes which are nonuniform in structure willbe soluble when polymerized; accordingly trimethylene sulfide has beenfound not to work, while in contrast Z-m'thyltrimethylene sulfidepolymerizes under the conditions of the present method. The preferredpolymerization solvents are polar and are selected from one of threedifferent groups. Group 1 consists of tetrahydrofuran, di-ethyl ether,tetrahydropyrane and other cyclic or linear ethers alone or incombination which are liquids at low temperatures and pressures. Group 2consists of mixtures of ethers and alkanes which are liquids at lowtemperatures and pressures in the ratio of approximately 50/50 such ashexane and tetrahydrofuran or pentane and tetrahydrofuran. Group 3consists of alkanes preferably having from -12 carbon atoms and 1 to 5volume percent hexamethylphosphortriamide or the t-amines. A solventfrom the latter group promotes both the initiation rate and thepropagation rate.

The polymerization is initiated at about 80 C. or lower in order toassure formation of the carbanion species. While the polymerizationtemperature range in the reaction vessel is between 80 to 0 C.,initiation at 80 C. or below, with a subsequent rise to -40 C. duringpolymerization is preferred. Owing to the highly reactive nature of thecarbanion it is imperative that the reaction vessel be free from activehydrogens and compounds such as water. For this reason thepolymerization, according to the preferred method, is carried out in ahigh vacuum so as to be substantially free from active hydrogens, suchas on the order of torr. Or, if preferred, an inert atmosphere such asnitrogen may be utilized in lieu of the high vacuum.

Under the aforementioned conditions the thietane represented in F above,is attacked by the organolithium initiator RLi, at the sulfur atomresulting in a ring opening to produce a primary carbanion specieshaving the general formula:

Each of the carbanions thus formed will react repetitively with excessthietane to yield a linear polymer having the general formula:

R1 a Ra [s t t t] L.

1 1: its its =+i a) wherein X is an integer of at least 160 up toapproximately 12,000. It is to be understood that the molecular weightof the polythietane F is dependent upon the ratio of catalyst to monomerselected.

If a di-lithium initiator is selected the polythietane will have twoprimary carbanions, one at either end. The primary carbanions, formedwith either initiator, are capable of initiating vinyl-substitutedstyrene monomers having up to about 12 carbon atoms to form blockcopolymers. Representative monomers are styrene, the alkylstyrenes suchas a-methylstyrene, 4-isopropylstyrene, 4-tbutylstyrene and the like.The nitriles such as acrylonitrile, ethacrylonitrile andmethacrylonitrile and the like may also be polymerized.

To form a triblock copolymer of the general type ABA wherein Arepresents the vinyl substituted polymer and B represents the thietanepolymer it is possible to first initiate the A constituent with anorganolithium catalyst.

When polymerization is complete the B or thietane constituent is thenadded and it will grow to form a block copolymer of the type AB. At thisstage the thietane portion will have a terminal primary carbanion. Thuswith a subsequent charge of the A, vinyl-substituted monomer, a thirdpolymerization will take place resulting in the final ABA triblockcopolymer.

Alternatively, the thietane may be initiated first with a dilithiumcatalyst. After polymerization thereof, a subsequent charge of thevinyl-substituted monomer will be polymerized by both carbanions of thethietane resulting in the ABA triblock copolymer.

The ABA triblock copolymer formed by either method yields a producthaving unexpected but excellent ozone resistance and outstanding thermalstability. It may be used where elasticity, comparable to that of rubberis required, yet quite unlike rubber, vulcanization is not necessarysince the triblock copolymers although having a rubber central portionhave the totally unexpected processing property of behaving as athermoplastic. The polymer thus formed may be utilized generally in lieuof rubber compounds and specifically in extrusion molding, injectionmolding processes and the like to produce such items as heels, toys andbottle caps and the like and does not require curing. Degradationmeasurements made in air have shown that this polymer chain maintainsits integrity up to at least 240 C.

It has been found desirable to form the B or central unit with amolecular weight of generally around 50,000 to 200,000 which will easilyflow in molding processes. At the upper limit, i.e., about 1,000,000molecular weight, the polymer would be difiicult to mold whereas thelower limit, i.e., 40,000 molecular weight would be deleterious to theelastomeric properties. A good average molecular weight for the A or endunits ranges from 10,000 to 20,- 000.

The following five examples recite the preparation of ABA triblockcopolymers utilizing mono and dilithium initiators. All reactions wereconducted at approximately to 40 C. and under a vacuum on the order of10* torr. Also recorded are the tensile strength and elongation ratio ofthe final block copolymer. Degradation of the polymer chain occurred atapproximately 290 C. under a vacuum.

EXAMPLE I Into a suitable reaction vessel was charged 3.5 grams ofstyrene and 0.2 millimoles of n-butyllithium in mls. of tetrahydrofuran.Temperature within the reaction vessel during polymerization wasmaintained at -50 C. Following the polymerization of the styrene, 14grams of a-methyltrimethylene sulfide was added and allowed to reactwith the polystyrene for 24 hours. Upon completion of the formation ofthe polystyrene-polysulfide, or AB block copolymer, a second quantity,3.5 grams, of styrene was added to the reaction vessel and permitted topolymerize, the reaction being almost instantaneous. Subsequentexamination of the ABA triblock copolymer thus formed revealed a tensilestrength at break of 1500 lbs./in. and an elongation ratio of 11.

EXAMPLE II In a similar manner as described in Example I, but at 80 C.,2.5 grams of a-methylstyrene was initiated by 0.1 millimoles ofsec-butyllithium in 70 mls. of tetrahydrofuran. Following polymerizationof the oz-methylstyrene, 9 grams of a-methyltrimethylene sulfide wasadded and polymerized and then an alditional 2.5 grams ofa-methylstyrene was added and polymerized. The ABA triblock copolymerthus formed was found to have a tensile strength at break of 1400lbs/in. and an elongation ratio of 11.

EXAMPLE III In this reaction the B monomer, a-methyltrimethylenesulfide, was polymerized first by charging 10 grams into the reactionvessel with 0.2 millimoles of a dilithium adduct of 2,4-hexadiene in 85mls. of tetrahydrofuran at a temperature of -50 C. Polymerization of theB linear polymer was complete after 26 hours and 5 grams ofa-methylstyrene was then added and polymerized by the polysulfide toform the ABA triblock copolymer. Subsequent tests revealed a tensilestrength at break of 1400 lbs/in. and an elongation ratio of 10.

EXAMPLE IV In a similar manner as described in Example III, but at --80C., 10 grams of a-methyltrimethylene sulfide was charged into thereaction vessel with 0.3 millimoles of dilithium adduct of 2,4-hexadienein mls. of tetrahydrofuran. After 24 hours the polymerization wascomplete and 7 grams of a-methylstyrene was added yielding an ABAtriblock copolymer having a tensile strength at break of 1600 lbs/in.and an elongtaion ratio at break of 11.

EXAMPLE V In a similar manner as described in Examples III and IV, butat 40" C., 12 grams of a-methyltrimethylene sulfide was charged into thereaction vessel with 0.25 millimoles of a-methylstyrene dilithium in 150mls. of tetrahydrofuran. After 24 hours the polymerization was completeand 5 grams of a-methylstyrene was added yielding an ABA triblockcopolymer having a tensile strength at break of 1500 lbs./in. and anelongation ratio at break of 9.

It can be seen that the disclosed invention carries out the objects ofthe invention set forth above. As will be apparent to those skilled inthe art, many modifications can be made without departing from thespirit of the invention herein disclosed and described, the scope of theinvention being limited solely by the scope of the attached claims.

What is claimed is:

1. A method for the preparation of block copolymers of thietanes andvinyl-substituted monomers comprising the steps of: reducing thepressure within a reaction vessel to approximately torr so as tosubstantially eliminate any active hydrogen containing compounds,charging said vessel with a vinyl-substituted monomer, cooling andmaintaining said vessel at a temperature range of at least -80 C. toabout 0 C. charging a catalytic amount of monolithium organic initiatorinto said vessel, polymerizing the vinyl-substituted monomer, charging athietane monomer having the formula:

wherein R is selected from the group consisting of alkyl, aryl,cycloalkyl radicals and combinations thereof having from 1 to 9 carbonatoms and R to R are selected from the group consisting of hydrogen andalkyl, aryl, cycloalkyl radicals and combinations thereof having from 0to 9 carbon atoms, polymerizing the thietane to form a vinyl-thietanecarbanion terminated linear polymer, again charging a vinyl-substitutedmonomer into said vessel, forming a second vinyl polymer and therebyforming the vinyl-thietane-vinyl block copolymer.

2. A method for the preparation of block copolymers as in claim 1,wherein R is a methyl radical and R to R are hydrogen.

3. A method for the preparation of block copolymers as in claim 1,wherein said monolithium organic compound has the general formula RLiwherein R is selected from the class consisting of aliphatic,cycloaliphatic and aromatic radicals having from 1 to about 20 carbonatoms.

4. A method for the preparation of block copolymers as in claim 3,wherein R is selected from the class consisting of methyllithium,ethyllithium, and the isomers of propyllithium, and butyllithium.

5. A method for the preparation of block copolymers as in claim 1,wherein the preferred temperature is at least from C. to about 40 C.

6. A method for the preparation of block copolymers as in claim 1,wherein the vinyl-substituted monomers are selected from the classconsisting of styrene monomers and substituted styrene monomers havingup to about 12 carbon atoms.

7. A method for the preparation of block copolymers as in claim 6,wherein the substituted styrene monomers are selected from the classconsisting of styrene, a-methylstyrene, 4-isopropylstyrene and4-t-butylstyrene.

8. A composition of matter comprising a block copolymer having thegeneral configuration ABA wherein each A block is a vinyl-substitutedpolymer having an average molecular weight of 10,000 to 20,000 and isselected from the class consisting of styrene monomers, substitutedstyrene monomers having up to about 12 carbon atoms and nitrile monomersand the B block is derived from a thietane having an average molecularweight of 50,000 to 200,000 and having a repeating unit represented bythe formula:

L 1'. t. id

wherein R is selected from the group consisting of alkyl, aryl,cycloalkyl radicals and combinations thereof having from 1 to 9 carbonatoms and R to R are selected from the group consisting of hydrogen andalkyl, aryl, cycloalkyl radicals and combinations thereof having from 0to 9 carbon atoms, said ABA block copolymer having an average tensilestrength of from about 1400 pounds per square inch to about 1600 poundsper square inch and an average elongation ratio of from about 9 to about11. 9. A block copolymer as in claim 8 wherein the A blocks arepolystyrene and the B block is polymethyltrimethylene sulfide andwherein said block copolymer has a high degree of ozone resistance andthermal stability maintaining its integrity up to about 240 C. in air.

References Cited UNITED STATES PATENTS 6/1967 Edmonds, Jr. 260-79 OTHERREFERENCES MELVYN I. MARQUIS, Primary Examiner U.S. Cl. X.R.

